Marian Smoluchowski
Institute of Physics

Jagiellonian University

Diploma thesis

Studies of control samples and backgrounds for the measurement of direct CP violation with interferometric methods at KLOE

Supervisor: dr Eryk Czerwiński

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abstract

Defence year: 2023

The main goal of these studies is to determine a correction factor for the efficiency of selection obtained using KSKL -> pi+pi-pi0pi0 Monte Carlo events using experimentally collected data in the function of time difference Deltat between decays of kaons. It constitutes a continuation of an analysis for Re(epsilon'/epsilon) and Im(epsilon'/epsilon) parameters, which began in [1]. Measurement principle is based on the selection of background channels having common properties with KSKL -> pi+pi-pi0pi0. The chosen decays were KSKL -> pi+/-l-/+nipi0pi0, KSKL -> pi+pi-3pi0 and KSKL -> pi+pi-pi+pi- corresponding to signal-like parts K -> pi0pi0, K -> pi+pi-, respectively. The first step was to perform a selection under the hypothesis of each tagging decay (K -> pi+/-l-/+nipi0pi0, KL -> 3pi0 and KS -> pi+pi-) and reach the highest possible purity. Then, the number of tagging events was weighted with a branching ratio for each signal-like part to obtain so-called expected distributions of the time difference. The additional selection under the hypothesis of K -> pi0pi0 or K -> pi+pi- was imposed on the events after tagging to mimic the selection performed for KSKL -> pi+pi-pi0pi0 using MC. Importantly, independence between charged and neutral parts of decay had to be conserved, so the method of trilateration was adapted to reconstruct a neutral vertex. Finally, having determined the expected and selected distributions of Deltat, a correction factor can be calculated via the division of efficiency obtained from data by the efficiency from MC. The result is not a uniform distribution, so there exists a specific factor for each bin of the Deltat histogram. Final uncertainties were determined using a standard propagation of a measurement error. A measured correction will be used in the further studies over CP symmetry breaking in the entangled kaons? systems.

Publications

ARTICLES CONFERENCE PROCEEDINGS

1. Direct tests of T, CP, CPT symmetries in transitions of neutral K mesons with the KLOE experiment
   D. Babusci, M. Berłowski, C. Bloise, F. Bossi, P. Branchini, B. Cao, F. Ceradini, P. Ciambrone, F. Curciarello, E. Czerwiński, G. D'Agostini, R. D'Amico, E. Dane, V. De Leo, E. De Lucia, A. De Santis, P. De Simone, A. Di Domenico, E. Diociaiuti, D. Domenici, A. D'Uffizi, G. Fantini, A. Gajos, S. Gamrat, P. Gauzzi, S. Giovannella, E. Graziani, X. Kang, A. Kupść, G. Mandaglio, M. Martini, S. Miscetti, P. Moskal, A. Passeri, E. Pérez del Río, M. Schioppa, A. Selce, M. Silarski, F. Sirghi, E.P. Solodov, W. Wiślicki, M. Wolke, J. Bernabéu
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   abstract

   Phys. Lett. B 845 (2023) 138164
   Tests of the T, CPand CPTsymmetries in the neutral kaon system are performed by the direct comparison of the probabilities of a kaon transition process to its symmetry-conjugate. The exchange of inand outstates required for a genuine test involving an antiunitary transformation implied by time-reversal is implemented exploiting the entanglement of K0K0 pairs produced at a ?-factory. A data sample collected by the KLOE experiment at DAFNE corresponding to an integrated luminosity of about 1.7 fb?1 is analysed to study the Dt distributions of the ??KSKL??+????e??and ??KSKL???e??3?0 processes, with Dt the difference of the kaon decay times. A comparison of the measured Dt distributions in the asymptotic region Dt>>t? Sallows to test for the first time T and CPT symmetries in kaon transitions with a precision of few percent, and to observe CP violation with this novel method.

1. Test of T, CP, and CPT Discrete Symmetries via Kaons' Transitions at KLOE-2
   S. Gamrat
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   published in: Acta Phys. Pol. B Proc. Suppl. 17 (2024) 7-A4
   Pairs of neutral kaons produced at the DAFNE collider allowed to perform the first model-independent direct test of T, CP, and CPT symmetries utilizing the oscillations between the flavor and CP eigenbases. The analysis of 1.7fb^-1 data collected in 2004?2005 in the KLOE experiment led to the determination of ratios and double ratios of kaons? decay rates, establishing a few percent precision of the measurement in a model-free manner.